The present invention relates to a sintered alloy for valve seat having excellent wear resistance and a method for producing the same. More particularly, it relates to an iron base sintered alloy comprising vanadium carbide(VC) particles, Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy particles and Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy particles in which the composition is dispersed in a structure of sorbite and a method for producing the same, thus being suitable for use as materials of valve seats for automotive engines which requires excellent wear resistance, high-performance, high-rotation-speed and low-fuel-consumption.
A valve seat for an automotive engine, which is an engine part to increase thermal efficiency of a combustion chamber, is required to have high heat resistance, high wear resistance and high oxidation resistance at a temperature of from 400xc2x0 C. to 700xc2x0 C. to suffer from contact, friction, exposure to exhaust gas during the operation of the internal combustion engine.
Methods for producing valve seats of automotive engines are an infiltration process, a hard metal addition process, a control of alloy composition and the like.
An infiltration is the process of filling pores of a sintered alloy material with infiltrating materials such as Cu, and Cuxe2x80x94Pd, or solid lubricants such as Pb, PbO, B2O3, ZnO and the like and thus it improves ductility and machinability when valves are rotating.
A hard metal addition is the process of producing a sintered alloy containing hard Fexe2x80x94Mo, or Coxe2x80x94Nixe2x80x94Wxe2x80x94C carbide complex having about 300 xcexcm of size. The sintered alloy containing hard carbide complex improves wear resistance by dispersing heavy loading to valve seat through hard carbides having excellent wear resistance when valves are rotating. However, it has several disadvantages such as poor machinability, and use of a large quantity of expensive Co, Ni, W which increases total manufacturing cost.
A control of alloy composition is the process of mixing alloy components as elemental powder, and then melting the powders to form an alloy of a certain composition. It is low in price and easy to produce but difficult to obtain homogeneous structure. Metals such as Co, Ni, Mo, Cr, W and the like are usually used and a large quantity of Co is used to increase thermal stability.
A conventional process of producing sintered alloy includes the steps of mixing each component, compacting the mixture, sintering the compacted mixture, copper infiltration into the sintered mixture, followed by heat treatment. This is a known powder metallurgy manufacturing process. In this process for manufacturing a sintered alloy for a valve seat, Coxe2x80x94Moxe2x80x94Cr alloy powder or Coxe2x80x94Nixe2x80x94Wxe2x80x94C alloy powder is added to Fe powder to improve wear resistance. However, the sintered alloy produced by this method still has unsatisfied wear resistance to use as materials for valve seats of engines which requires high-performance and high-rotation-speed.
In order to reduce abrasion of valve seat, a gasoline containing 0.2 to 0.8 g/gallon of tetraethyl lead has been used as an anti-knocking agent by increasing octane number. This anti-knocking agent also formed a lubricating film between valve and valve seat by producing lead oxide or lead compound after combustion. However, it is recently a compulsory regulation to use unleaded gasoline containing not higher than 0.004 g/gallon of tetraethyl lead due to serious pollution associated with carbon monoxide, carbon dioxide and lead. It is, therefore, highly desirable to provide novel materials for valve seats of automotive engines having an improved wear resistance compared to the conventional ones.
The inventors have developed a sintered alloy composition for valve seats having an improved wear resistance to satisfy the requirements for engines to suffer from high output, high rotation and low fuel consumption.
The present invention relates to a sintered alloy composition for valve seats having excellent wear resistance, homogeneous sintered structure and cost effectiveness, in which vanadium carbide particles, Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy particles and Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy particles are dispersed in a structure of sorbite.
In one embodiment, the invention relates to a sintered alloy comprising:
between about 0.7 to about 1.3 weight % of vanadium carbide particles;
between about 84 to about 86 weight % of Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy particles; and
between about 12.5 to about 13.5 weight % of Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy particles.
The sintered alloy may further include between about 0.6 to about 1.3 weight % of added carbon, wherein the particles are dispersed in a structure of sorbite. The Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy powder advantageously comprises about 86 to about 93 weight % of Fe; about 5 to about 8 weight % of Co; about 1 to about 3 weight % of Ni; and about 1 to about 3 weight % of Mo. The Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy powder advantageously comprises about 48 to about 80 weight % of Cr; about 8 to about 25 weight % of W; about 10 to about 25 weight % of Co; and about 1 to about 3 weight % of C. The sintered alloy advantageously further includes between about 11 to about 18 weight % of added infiltrating material. The infiltrating material advantageously includes copper. The infiltrating material may in one embodiment be selected from the group consisting of Cu, a Cuxe2x80x94Pd alloy, Pb, PbO, B2O3, ZnO, or mixtures thereof. The sintered alloy advantageously further includes added carbon, for example added in the form of graphite particles. Advantageously, the Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy powder consists essentially of about 86 to about 93 weight % of Fe; about 5 to about 8 weight % of Co; about 1 to about 3 weight % of Ni; and about 1 to about 3 weight % of Mo; and the Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy powder consists essentially of about 48 to about 80 weight % of Cr; about 8 to about 25 weight % of W; about 10 to about 25 weight % of Co; and about 1 to about 3 weight % of C. The sintered alloy composition is:
between about 1 to about 1.5 weight % of C;
between about 1 to about 3 weight % of Ni;
between about 6 to about 11 weight % of Cr;
between about 1 to about 3 weight % of Mo;
between about 5 to about 11 weight % of Co;
between about 1 to about 3 weight % of W;
between about 0.5 to about 1.0 weight % of V;
between about 11 to about 18 weight % of Cu; and
the balance Fe.
Advantageously, a valve seat for automotive engines is machined from the sintered alloy.
In another embodiment, the sintered alloy includes:
at least about 0.7 weight % of metal-carbide particles;
Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy particles, wherein the Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy particles contain an alloy comprising about 86 to about 93 weight % of Fe, about 5 to about 8 weight % of Co, about 1 to about 3 weight % of Ni, and about 1 to about 3 weight % of Mo;
at least 11.5 weight % of Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy particles, wherein the Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy particles contain an alloy comprising about 48 to about 80 weight % of Cr, about 8 to about 25 weight % of W, about 10 to about 25 weight % of Co, and about 1 to about 3 weight % of C, wherein the metal-carbide particles, Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy particles, and Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy particles are mixed and then are sintered into a substantially homogeneous porous structure; and
an infiltrating material disposed in the porous structure.
The sintered alloy advantageously further includes between about 0.6 to about 1.3 weight % of added carbon. The sintered particles are dispersed in a structure of sorbite, and the infiltrating material is advantageously Cu. The infiltrating material in one embodiment is selected from the group consisting of Cu, a Cuxe2x80x94Pd alloy, Pb, PbO, B2O3, ZnO, or mixtures thereof. Advantageously, the metal-carbide comprises vanadium carbide. In one embodiment, the sintered alloy had added carbon that was added in the form of graphite particles which were sintered into the sorbite structure, and the sintered alloy includes between about 11 to about 18 weight % of infiltrating material.
The invention also relates to a method for producing the sintered alloy for valve seat comprising the steps of:
mixing 84 to 86 weight % of Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy powder, 12.5 to 13.5 weight % of Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy powder, 0.7 to 1.3 weight % of vanadium carbide powder, and 0.6 to 1.3 weight % of graphite powder to form a substantially homogeneous mixture;
applying pressure and heat to the substantially homogeneous mixture in amounts sufficient to sinter the substantially homogeneous mixture into a porous sintered composition;
infiltrating with an infiltration material to form an infiltrated sintered alloy; and
quenching the infiltrated sintered alloy.
The method advantageously includes a surface pressure of from 5 to 8 ton/cm2 applied prior to and/or during sintering, and advantageously the sintering is performed at a temperature of from about 1160xc2x0 C. to about 1200xc2x0 C. under a reductive atmosphere. The reductive atmosphere advantageously includes ammonium gas, cracked ammonia gas, or a mixture thereof. The infiltrating material advantageously comprises copper, and the infiltration temperature is advantageously between about 1080xc2x0 C. to about 1100xc2x0 C. The quenching comprises oil quenching at a temperature of from about 850xc2x0 C. to about 880xc2x0 C. for 30 to 45 minutes. The method further advantageously includes tempering the quenched sintered alloy, wherein the tempering comprises maintaining the sintered alloy at a temperature of from about 590xc2x0 C. to about 610xc2x0 C. The substantially homogenous mixture in one embodiment further comprises iron or an iron alloy different than the Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy powder, wherein the iron or an iron alloy form on sintering a sorbite structure with the Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy powder, Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy powder, vanadium carbide powder, and graphite powder dispersed therein. The sintered alloy advantageously comprises:
Fe,
between about 1.0 to about 1.5 weight % of C,
between about 1 to about 3 weight % of Ni,
between about 6 to about 11 weight % of Cr,
between about 1 to about 3 weight % of Mo,
between about 5 to about 11 weight % of Co,
between about 1 to about 3 weight % of W,
between about 0.5 to about 1.0 weight % of V, and
between about 11 to about 18 weight % of an infiltrating material comprising Cu.
Advantageously, the Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy particles contain an alloy comprising about 86 to about 93 weight % of Fe, about 5 to about 8 weight % of Co, about 1 to about 3 weight % of Ni, and about 1 to about 3 weight % of Mo.
Advantageously, the Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy particles contain an alloy comprising about 48 to about 80 weight % of Cr, about 8 to about 25 weight % of W, about 10 to about 25 weight % of Co, and about 1 to about 3 weight % of C.
Advantageously, a surface pressure of from 5 to 8 ton/cm2 is applied prior to and/or during sintering, and the sintering is performed at a temperature of from about 1160xc2x0 C. to about 1200xc2x0 C. under a reductive atmosphere comprising ammonium gas, cracked ammonia gas, or a mixture thereof.
Advantageously, the infiltrating material comprises copper, and the infiltration temperature is between about 1080xc2x0 C. to about 1100xc2x0 C.
Advantageously, the quenching comprises oil quenching at a temperature of from about 850xc2x0 C. to about 880xc2x0 C. for 30 to 45 minutes.
Advantageously, the method further includes tempering the quenched sintered alloy, wherein the tempering comprises maintaining the sintered alloy at a temperature of at least about 590xc2x0 C. for at least about 2 hours.
In one embodiment, the present invention is a sintered alloy for valve seats prepared by dispersing:
0.7 to 1.3 weight % of a vanadium carbide powder;
84 to 86 weight % of a Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy powder;
12.5 to 13.5 weight % of a Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy powder; and
0.6 to 1.3 weight % of graphite powder in a structure of sorbite.
In one embodiment, the sintered alloy of the present invention is prepared by dispersing vanadium carbide particles, Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy particles and Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy particles in a structure of sorbite. In another embodiment, the present invention relates to the above-described alloys into which an infiltrating material is caused to infiltrate.
In one embodiment, the present invention is an alloy prepared by mixing, sintering, and heat treating a composition containing: 0.7 to 1.3 weight % of a vanadium carbide powder; 84 to 86 weight % of a base alloy that is a Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy powder; 12.5 to 13.5 weight % of a Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy powder; and 0.6 to 1.3 weight % of graphite powder. In one embodiment, the sintered alloy of the present invention is prepared by dispersing vanadium carbide particles, Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy particles and Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy particles in a structure of sorbite. In another embodiment, the present invention relates to the above-described alloy into which an infiltrating material is caused to infiltrate.
The present invention also relates to a method for producing the sintered alloy for valve seats comprising the steps of: mixing a Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo base alloy powder, a Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy powder, a vanadium carbide powder, and a graphite powder; sintering the mixture under the reductive atmosphere; adding an infiltrating material; and tempering.
The present invention also relates to a method for producing the sintered alloy for valve seats comprising the steps of: mixing a Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy powder, a Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy powder, a vanadium carbide powder, and a graphite powder with a composition comprising sorbite; sintering the mixture under the reductive atmosphere; adding an infiltrating material; and tempering.
In one embodiment, the sintered alloy of the present invention is prepared by dispersing vanadium carbide particles, Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy particles and Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy particles substantially homogenously in a structure of sorbite.
The present invention also relates to a method for producing the sintered alloy for valve seats comprising the steps of:
mixing 84 to 86 weight % of Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy powder, 12.5 to 13.5 weight % of Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy powder, 0.7 to 1.3 weight % of vanadium carbide powder, and 0.6 to 1.3 weight % of graphite powder;
applying a surface pressure of from 5 to 8 ton/cm2;
sintering at a temperature of from 1160xc2x0 C. to 1200xc2x0 C. under the reductive atmosphere containing ammonium gas;
infiltrating with an infiltration material, for example copper, at a temperature of from 1080xc2x0 C. to 1100xc2x0 C. and oil quenching at a temperature of from 850xc2x0 C. to 880xc2x0 C. for 30 to 45 minutes; and
tempering at a temperature of from 590xc2x0 C. to 610xc2x0 C.
In some embodiments, other components, such as particles containing Fexe2x80x94Mo, Coxe2x80x94Nixe2x80x94Wxe2x80x94C, Coxe2x80x94Moxe2x80x94Cr, and the like can be added. In the preferred embodiment, however, the sintered alloy is prepared by dispersing vanadium carbide particles, Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy particles, and optionally graphite particles, in a base of Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy particles which on sintering forms a sorbite structure.
Unlike conventional sintered alloys, in the preferred embodiments of this invention the sintered alloy requires use of alloys mixed with Fe instead of using individual Fe, Ni, Mo, and Co powder to provide homogenous structure by preventing from local segregation associated with the conventional sintered alloys.
In one embodiment, the invention comprises a sintered alloy containing a Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy powder. The Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy powder comprises:
86 to 93 weight %, for example 89 to 90 weight %, of Fe;
5 to 8 weight %, for example 6 to 7 weight %, of Co;
1 to 3 weight %, for example 1.5 to 2.5 weight %, of Ni; and
1 to 3 weight %, for example 1.5 to 2.5 weight %, of Mo.
In one embodiment, the invention comprises a sintered alloy containing a Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy powder. The Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy powder comprises:
48 to 80 weight %, for example 60 to 70 weight %, of Cr;
8 to 25 weight %, for example 12 to 20 weight %, of W;
10 to 25 weight %, for example 15 to 20 weight %, of Co; and
1 to 3 weight %, for example 1.5 to to 2.5 weight %, of C.
In one embodiment, the invention comprises a sintered alloy containing a Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy powder, a Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy powder, and a metal carbide powder. Metal carbides useful in the present invention include for example vanadium carbide, silicon carbide, tungsten carbide, molybdenum carbide, and mixtures thereof. Vanadium carbide is preferred.
In a preferred embodiment of the present invention, the Fexe2x80x94Coxe2x80x94Nixe2x80x94Mo alloy powder is preferably in a range of from 84 to 86 weight % against the total of the sintered alloy. If the amount is deviated from this range, the sintered alloy becomes inferior in wear resistance.
The Crxe2x80x94Wxe2x80x94Coxe2x80x94C alloy powder is preferably in a range of from 12.5 to 13.5 weight % against the total of the sintered alloy to improve the wear resistance by dispersing in the substrate structure. If the amount is less than 12.5 weight %, the sintered alloy becomes inferior in wear resistance. On the other hand if it is greater than 13.5 weight %, it is disadvantageous in cost.
The metal carbide powder is advantageously vanadium carbide. Vanadium is added as vanadium carbide powder to improve wear resistance by dispersing in the substrate structure. The vanadium carbide powder is preferably in a range of from 0.7 to 1.3 weight % against the total of the sintered alloy. If the amount is less than 0.7 weight %, it does not sufficiently improve wear resistance. On the other hand if it is greater than 1.3 weight %, it is disadvantageous in cost.
Advantageously the composition also includes graphite powder. The graphite powder is preferably in a range of from 0.6 to 1.3 weight % against the total of the sintered alloy. If the amount is less than 0.6 weight %, it does not affect to increase hardness. On the other hand if it is greater than 1.3 weight %, it becomes low in hardness.
An infiltrating material, for example copper, is added in a quantity up to the total amount that can be made to infiltrate the alloy. This amount will depend on the porosity and composition of the sintered particles.
Accordingly, in one embodiment an overall composition of the sintered alloy comprises 1.0 to 1.5 weight % of C, 1 to 3 weight % of Ni, 6 to 11 weight % of Cr, 1 to 3 weight % of Mo, 5 to 11 weight % of Co, 1 to 3 weight % of W, 0.5 to 1.0 weight % of V, 11 to 18 weight % of an infiltrating material, for example Cu, and balance consisting of Fe.
The sintered alloy for valve seats of the present invention is prepared by:
mixing the above powdered composition;
advantageously applying a surface pressure of from 5 to 8 ton/cm2 to have a compacting density of 6.8 g/cm2;
sintering, advantageously at a temperature of from 1160xc2x0 C. to 1200xc2x0 C. for 1 hour, and advantageously under the reductive atmosphere containing for example cracked ammonium gas;
infiltrating with an infiltrating material, for example a copper-containing infiltration material, advantageously at a temperature of from 1080xc2x0 C. to 1100xc2x0 C.,
advantageously oil quenching at a temperature of for example from 850xc2x0 C. to 880xc2x0 C. for 30 to 45 minutes; and
advantageously tempering, for example at a temperature of from 590xc2x0 C. to 610xc2x0 C.